When I first worked on an American aircraft of BAE manufacture, I questioned the foot rests on the instrument panel; I was told used in cruise, I note not visible on the B787 panel, but I would still suspect Pilots sit at the rear most seat position during cruise, than hunched over the control column, perhaps some actual Pilots might comment?
I can only speak for myself but I would feel negligent if I sat with the seat in the most aft position during cruise. I can also say that I can’t remember seeing my First Officers sitting with their seat right back either. I fly short haul though ( max five hour sector) so it may well be different with long haul pilots. My opinion is that the PF should be in a normal seating position at the least.